Answer: Essential elements are required by all plants and have specific metabolic roles; beneficial elements improve growth in some plants but are not universally required.
- A Essential and beneficial elements are sometimes mistakenly described as the exact same group of plant nutrients under two different historical names in general practice
- B Essential elements are required by all plants and have specific metabolic roles; beneficial elements improve growth in some plants but are not universally required
- C Beneficial elements are sometimes thought to become essential to plant survival mainly at unusually high soil concentrations as frequently described in most textbook accounts
- D Essential elements are sometimes thought to be obtained by plants mainly from atmospheric gases absorbed through the stomata during normal conditions as generally observed
Correct answer: B. Essential elements are required by all plants and have specific metabolic roles; beneficial elements improve growth in some plants but are not universally required
Explanation: Essential: required by all plants, specific metabolic role. Beneficial: improve growth/yield in some plants or under specific conditions but are not universally required. Examples of beneficial: Na (for C<sub>4</sub> plants), Si (strengthens cell walls), Co (for legumes for N<sub>2</sub> fixation).
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.